Solve three easy problems to Easy Prey award.

python/e719.py

@@ -0,0 +1,69 @@
+from typing import List, Optional
+from math import sqrt
+from functools import lru_cache
+
+
+def to_int(digits: List[int]) -> int:
+    return int("".join(map(str, digits)))
+
+
+def int_len(n: int) -> int:
+    return len(str(n))
+
+
+@lru_cache
+def digits_make_sum(digits, remainder: int) -> Optional[List]:
+    if len(digits) == 0:
+        if remainder == 0:
+            return []
+        return None
+
+    remainder_digits_count = int_len(remainder)
+    if remainder_digits_count > len(digits):
+        return None
+
+    if to_int(digits) < remainder:
+        return None
+
+    for group_size in range(1, remainder_digits_count + 1): 
+        digits_list = list(digits)
+        rest_value = remainder - to_int(digits_list[:group_size])
+        rest_digits = tuple(digits_list[group_size:])
+        r = digits_make_sum(rest_digits, rest_value)
+        if type(r) is list:
+            return [digits_list[:group_size]] + r
+    return None
+
+
+def digits_sum_to(digits, number: int):
+    r = digits_make_sum(digits, number)
+    if type(r) is list:
+        # print(digits, r, number)
+        return True
+    return False
+
+
+def t(limit: int) -> int:
+    r = 0
+    for base in range(4, int(sqrt(limit)) + 1):
+        n = base * base
+        n_digits = tuple(map(int, list(str(n))))
+        if digits_sum_to(n_digits, base):
+            r += n
+    return r
+
+
+def euler_719():
+    assert(t(10**4) == 41333)
+    assert(digits_sum_to((1, 0, 0), 10) == True)
+    assert(digits_sum_to((1, 8), 9) == True)
+    assert(digits_sum_to((2, 5), 5) == False)
+    assert(digits_sum_to((8, 2, 8, 1), 91) == True)
+    assert(t(10**6) == 10804656)
+    return t(10**12)
+
+
+if __name__ == "__main__":
+    solution = euler_719()
+    print("e719.py: " + str(solution))
+    assert(solution == 128088830547982)